Fuze



Sept.. 29, 1959 L.. R. HAFSTAD ETAI- 2,906,885

FUZE Original Filed Aug. 7, 1944 5 Sheets-Sheet l ur n i151( Sept. 29, 1959 L.. R. HAI-'STAD EIAL 2,906,886

FUZE

original Fild Aug. 7, 1944 5 Sheets-Sheet 2 INVENTORS LAWREIVGE' R. HA

BY FICHA ATT Sept 29, w59 L. R. HAFSTAD ETAL FUZE 5 Sheets-Sheet 3 Uriginal Filed Aug. 7, 1944 vm, hm.

@tief mk NEN@ INVENTORS LWRENCER. HAI-'STAD ROBERTS ev RICHARD B.

ATT

Sept. 29, E959 L. R. HAFSTAD EVAL 2,996,836

FUZE

5 Sheets-Sheet 4 Original Filed Aug. 7. 1944 I l (l .v/mwmwxwaw@ Y, 11....

mvENToRs LAWRENCE R. HAFSTD Sept. 29, 1959 1 R. HAFsTAD EVAL 2,906,885

FUZE

Original Filed Aug. 7. 1944 5 Sheets-Sheet 5 2,906,885 Fatented Sept. 29, 1959 tice FUZE Lawrence R. Hafstad and Richard B. Roberts, Washington, D1'.

Original application August 7, 1944, Serial No. $48,480. Divided and this application June 10, 1953, Serial No. 360,744

12 Claims. (Cl. Z50-237) This invention relates to photoelectric devices and has particular reference to a novel light-sensitive fuze for explosive projectiles. This application is a division of copending U.S. patent application Serial No. 548,480, tiled August 7, 1944, now abandoned, by the same inventors.

ln the use of a projectile against a target, such as an airplane, it is desired to cause the projectile to explode at the target or in the immediate vicinity thereof in order to produce maximum damage.

An object of the present invention, therefore, is to provide a fuze which may be readily attached to projectiles of various types and which will cause the projectile charge to explode when the projectile is Within damaging range of an airplane, or other target, and at the proper position so that the fragmentation cone will intercept the target.

Another object is to provide a fuze having a light-sensitive element connected in an electrical circuit so that a change in the quanitity of light striking the element, due to the fuze approaching the target, will fire a detonator, thereby causing the projectile to explode.

A further object of the invention resides in the provision of a light-sensitive fuze, the sensitivity of which is largely independent of the actual light intensity but which is sensitive to a given fractional change of the light intensity existing at the time of use.

An additional object is to provide a light-sensitive fuze having a window or lens which admits maximum light in a predetermined direction and has a narrow angle of optical field.

A further object is to provide a light-sensitive device which is equally sensitive to light striking the photoelectric cell from any angular position around the axis of the cell, at a predetermined inclination to the axis.

Another object of the invention is to provide an improved electrical circuit for use with a light-sensitive fuze.

Still another object of the invention is to provide a fuze having a squib operable by the plate current of a thyratron which is triggered by an amplified impulse from a photoelectric cell.

A still further object is to provide mechanical improvements for making a reliable and satisfactory light-sensitive fuze.

An additional object is to provide a light-sensitive fuze which may be,u'sed with a bomb, shell, or other explosive device vso that ground approach will cause the bomb, for instance, to explode and scatter fragments downward, for greater effectiveness against personnel.

These and other objects of the invention may be better understood by reference to the accompanying drawings, in which Figure ,lfis a longitudinal sectional view of one form of the new fuze adapted for use on a bomb;

`Figures 2-7, inclusive, are sectional views on the lines 2 2 to 7-7 inclusive, respectively, in Fig, 1;

posed between the sections.

Figure 8 is a detail sectional view on the line 8--8 in Figure 6, showing the arming and self-destruction switches;

Figure 9 is a side elevational view of a bomb, with parts broken away, showing the photoelectric proximity fuze mounted thereon and connected to the arming wire;

Figure 10 is a sectional view on the line 10--10 in Figure l;

Figure 11 is a sectional View on the line 11--11 in Figure, 5;

Figure 12 is a sectional View on the line 12-12 in Figure 1;

Figure 13 is a detail sectional view on the line 13-13 in Figure 7, showing plug and socket connections for coupling parts of the fuze, and

Figure 14 is a diagrammatic view of the wiring circuits for the fuze.

The new fuze is illustrated in a form suitable for use on the tail portion of a bomb, although it will be understood that the fuze may be used on the nose of the bomb and on other types of projectiles.

Referring to the drawings, the numeral 20 indicates the fuze casing which is of cylindrical shape and is formed of metal of suitable thickness to insure ruggedness. The casing 20 is open at its rear end where it receives a photoelectric cell unit 21 including rear and front sections 22 and 23, respectively, and a lens 24 disi The lens 24 is of annular shape, having a convex outer lens face 24a. The adjacent faces of the sections 22 and 23 are provided with annular, marginal recesses 22a and 23a, respectively, for receiving the ends of the lens, and the sections 22 and 23 are secured to the lens by suitable bolts (not shown) extending through the sections and the lens. Thus, the lens is held firmly in a fixed position relative to the sections 22 and 23.

The rear section 22 is provided with an axially disposed cup 25 which is open at its front end. The side wall of the cup extends forwardly a substantial distance from the section 22 and terminates in a straight, annular rim 26 which is disposed substantially medially of the ends of the unit 21. The front section 23 is formed with a rearwardly extending axial sleeve 27 terminating in an annular rim 28, the rims 26 and 28 cooperating to define an annular light slit 29 within the central portion of the lens 24. The front section 23 is also provided near its periphery with a forwardly extending sleeve 23b which ts closely in the open rear end of the casing 20. The photoelectric unit 21 is held in the casing by a plurality of screws 20a extending through the casing and threaded into the sleeve 23b.

Mounted in the sleeve 27 and extending into the cup 25 is a photoelectric tube or photo-voltaic cell 32 having its cathode or light sensitive element 32a disposed slightly to the rear of the slit 29. A clamping ring 33 is secured to the front face of section 23, as by means of screws 33a, and serves to hold the tube in position against an annular inclined surface 23C on the section. The tube 32 is cushioned by means of annular rubber pads 34 and 35 disposed between the annulus of the tube and the surface 23e and the ring 33, respectively. The tube 32 may be of any suitable construction, such as that shown in a copending application of I. E. Henderson et al., Serial Number 568,020, filed December 13, 1944.

Connected to the front section 23 of the photoelectric cell unit 21 is a frame including opposed side rails 36, the rear ends'of which are doubled over and secured to the sleeve 2312 by means of screws 37. At their front ends, the rails 36 are bent inwardly and secured to the rear face of an insulating plate 38, as by means of bolts 39 and nuts 40. Mounted on the rear face of the plate 38 is a clockwork Ymechanism 42 which may be of conventional design. The clock mechanism 42 is normally locked against operation by a transverse plunger 43 (Fig. which is urged outwardly toward a clock-releasing position by a compression spring 44. The plunger 43 is slidably mounted in a bracket 45 secured to the insulating plate 38, and the spring 44 isrseated at lits inner end on-the bracket 45 and at its outer end against a button 46 on the plunger. At its outer end, the button 46 engages a stop v47 slidably mounted in a hollow boss 48 on the casing 20. Y The stop 47 is normally held against outward movement in the boss by means of an arming wire 49 extending transversely through the boss, whereby the plunger 43 is held in its retracted position for locking the clock 42 against operation. YThe stop 47 is retained in the boss 48 by a pin 50 extending transversely through the boss and through a longitudinal slot in the stop. It will be apparent that when the arming wire 49 is-withdrawn from the boss 48,'the stop 47 is released and allows the spring 44 to move plunger 43 outwardly so as to release the clock. y

A bail 51 is pivotally mounted on a pin 51a on the bracket 45, and before the fuze is assembled in the casing 28, the plunger 43 is pressed inwardly against spring 44 to its clock-locking position where it is held temporarily by swinging the bail 51 on its pivot until the transverse portion of the bail overlies the plunger button 46. The plunger 43 is then released, and as the fuze parts including plate 38 and rails 36 are inserted in casing 2t), the rear end of the-.casing engages the transverse portion of bail 51 and forces it rearwardly out of line with the plunger 43. The latter is then held in its retracted position by the inner wall of the casing 20 until the fuze assembly including plate 38 and rails 36 reaches its 'innermost position in case 20, where the plunger is held retracted by engagement with the stop 47,

The'clock mechanism 42 includes a driven shaft 42a which extends throughY the plate 38 and is adapted to opcrate a switch assembly 53 including an arming switch 54 and a self-destruction switch 55 mounted on the front Yface of plate 38. AnV insulating segment 56 is mounted onthe front end ofclo-ck shaft 42a and is normally positioned between contact springs forming the switches 54 65 forms the front end of the battery easing, and the legs of` the frame 65 are disposed in closely adjacent relation to the inner wall of casing 20. A retaining plate 67 is secured to each of the legs of .the frame 65. Between the retaining plates 67 are the battery elements which comprise an A battery 68, a B battery 69 made up of a plurality of serially connected cells, a C battery 70 (Figure 14), and a battery condenser 71. The condenser and the cells constituting the A, B and C batteries lare encased in a potting compo-und 72 which provides suitable insulation fand protection against the elements. lt also serves to protect the .parts against mechanical shock. Y'

An amplifier and thyratron unit 74 is disposed in the casing between the cell unit 21 and the clock mechanism 42, the unit '74 being electrically connected by wiring 75 through the plug 58, sockets 60 and wiring 63 to the battery lunit 64. The amplier and thyratron unit 74 is mounted on an insulating plate 76 secured to the rails and 55.-. That'is, the arming switch 54 includes a pair f of switch spring 54a and 54b (Figure 8) which are normally separated from each by the segment 56, and the self-destruction switch 55 includes a pair of switch springs 55a and 55b which also are normally separated by the segment 56, wherebythe switches are held open. When plunger 43 releases the clock mechanism 42, the latter drives the `insulating segment 56 which, after a predetermined period of time, disengages the arming switch springs 54a and 54h, thereby causing the arming switch to close. Further rotation of segment 56 causes the selfdestructionswitch 55 to close after an additional time interval, due to-disengagement of the segment from the switch springs 55aand 55b.

36 by brackets 77 and 7 7a, respectively the brackets being connected to the rails by screws 78.:V A resilient pad 79 is folded around the insulating plate 76 adjacent each of the brackets 77`and 77a, the insulating plate and pads being connected to the brackets by bolts 80. Thus, the plate 76 is resiliently connected to the side rails 36 through brackets 77 and 77a, whereby the .amplifier and thyratron unitis better adapted to withstand mechanical shock.

The amplier and thyratron unit 74 includes amplier tubes 82, 83 `and 84 and a thyratro-n 85. The tubes 82 to 85, inclusive, are held in position on the rear face of plate 76.by clips 86 or other suitable material. As shown in Fig. l0, the clips 86 are secured to the rear face of plate'76 by rivets 87 which extend through the plate and also serve to connect a retaining strap'88 to the front face of`plate 76. The end portions of strap 88 extend forwardly and are interconnected by a strip 89, the ends of which are turned over the ends of strap S8, as shown at 89a. Thus, the strap 88 and. the interconnecting strip 89 form a retainer for the necessary'resistors, condensers and other components 90, all of which may be encased as a unit'in a suitable potting compound (not shown). t

The tubes 82 to 85, inclusive,V the resistors and condensers 98,V and the batteries 68, 69, and 70 areY` electrically connected with the tube 32 and switches 54 and 55 in a circuit which is shown diagrammatically in Fig. 14. As there shown, the cathode 32a of the tube 32 is connected through a resistor 92 and one of the prong and socket connections 58a, 60 to a tap 93 on the B battery 69, while the anode of the tube 32 is connected to the control grid 82a of the first ampliier tube 82. One terminal of sacher the tube filaments szb, sab, s4b and ssb An electrical plug 58 is mounted in an opening in in- Y is connected by a wire 94 through another prong and socket connection 58a, 60 to the positive side of A battery 68, and the other terminal of each tube lament is connected by a wire 95 to a terminal 95a which, in turn, is connected to the plunger 43. The plunger 43,

' which is grounded to the battery casing 20, forms one element of a switch, the other element of which cornprises a pair of switch arms 96 mounted on the insulating plate 38, When the plunger 43 is in its normal retracted position, it is out of engagement with the spring arms 916, so that "the switch 43, 96 lis openf However, when'the plunger 43 is released by arming wire 49, itienlgages the springarms 96l so as to complete the circuit from the tube filaments toV the negative sideof A battheir front ends, the rivets 62 are connected to wiring' 63, V

as by means of soldered joints.

, The plate 6l forms the rear end of a battery 'casing 64 which includes a generally U-shaped frame 65. The ends of the leg portions of the frame 65' 'are bent inwardly, as

tery' 68.

,The screen grids` 82e, 83e, and 84c.of the amplifier tubesvare connected-.through a wire 97 toJ aV second tap 93a on the B battery 69. Each of the tube plates 82d, 83dand'84d is connected through a load resistor 98 and shunt condenser 98a to a'wire 99 which Vleads through another of the' prongV and socket connections 58a, 60 to the positive' side of B battery 69, an additional load 5 resistor 100 being interposed between the wire 99 and the load resistor 98 for the third amplifier tube 84. It is the purpose of the resistor 100 and condenser 71 combination to provide a heavy filter for filtering out battery noises and transients and to attenuate the low frequency signals needed to subsequently fire the detonator unit. A wire 101 is connected between the resistors 98 and 100 and passes through battery condenser 71 to a coml mon battery terminal 102 connected to the negative side of the B battery 69, the positive side of C battery 70 and the negative side of A battery 68.

Grid resistors 90a are connected between the control grids of the amplifier tubes 82, 83 and 84 and the wire 95 to provide the proper bias on the grids. The amplier tubes are coupled by coupling condensers 90b and resistors 90C, and the output .of the third amplifierV tube 84 is coupled to the control grid 85a of the thyratron by another coupling condenser 90b. A by-pass condenser 90d is coupled between the wire 95 and each of the control grids 83a and 84a. The control grid 85a of the thyratron is connected through a grid bias resistor 103 and wire 104 to the negative side of C battery 70, so that the proper bias is imposed upon the thyratron grid. A by-pass condenser 105 is coupled between the thyratron plate 85d and wire 95.

The output of thyratron 85 is conducted through wire 106 and arming switch 54a, 54h to one side of an electrically operable squib or detonator 107, the other side of which is connected to wire 99 and the positive side of B battery 69. The contract arm 55a of the selfdestruction switch 55 is connected through a resistor 108 to a point between the squib 107 and the arming switch 54, the other contact 55b of the self-destruction switch being connected through a wire 109 to the terminal 95a. It will be apparent that when arming switch 54 is closed, as previously described, the squib 107 is connected at one side to the positive terminal of battery 69 and at the other side through switch 54 to the plate of thyratron 85, the filament of which is connected to the negative side of battery 69. Accordingly, when the thyratron is triggered, the detonator 107 is operated. Also, if the detonator 107 has not been operated prior to closing of the self-destruction switch 55, as previously described, the latter switch upon closing will complete a detonating circuit from the positive side of battery 69 through the detonator 107, resistor 108, self-destruction switch 55, terminal 95a, and switch 43-96 to the negative side of battery 69.

In the use of the new fuze, as shown, the casing 20 is mounted on the tail portion of a bomb 110, the front end of the casing fitting closely in an adaptor 111 on the bomb. The adaptor 111 is slit longitudinally, and the segments defined by the slits are clamped together against casing 20 by a releasable clamping ring 111a. The fuze casing 20 is housed within and protected by a tail assembly 112 on the bomb, the photo-electric unit 21 projecting rearwardly from the rear end of the tail assembly. In the nose portion of the bomb 110 is the usual mechanical fuze 113 which may be used in lieu of or in conjunction with the proximity fuze 20. The fuze 113 is armed by a propeller 114 which is normally locked by the arming wire 49 extending along the bomb casing and through the hollow boss 48, the intermediate portion of the arming Wire 49 being connected to a fixture 115 on the airplane or other vehicle carrying the bomb.

In operation, when the bomb is released, the arming wire 49 is withdrawn from the propeller 114 and from the hollow boss 48, thus releasing the propeller 114 and allowing plunger 43 of the proximity fuze to move outwardly under the action of spring 44. As a result, the clock mechanism 42 is started in operation and the switch 43--96 is closed. Upon closing of the switch l43--96, 'the filaments of tubes 82, 83, 84 and 85 are connected across "A battery 68 and are heated so that the fuz'e is prepared for operation upon closing of the arming switch 54. It has been found that for safety purposes the arming switch 54 should remain open for approximately six seconds after releasing the bomb, at which time the bomb will be approximately 600 feet below the bombing plane. It will be understood that safety devices other than and in addition to the switches 43-96 and 54a54b may be used.

The operation of the fuze is dependent upon the percentage change in the quantity of light reaching the lens 24 and the light-sensitive element of the tube 32, within a narrow angle which may be called the width of transmission zone and which may be defined as the angular separation between two directions in a plane through the axis of the fuze, in each of which the transmission of the lens-slit system is'half the maximum transmission. The forward angle is defined as the angle between a l plane normal to the axis of the fuze and a line midway between the two directions defining the transmission zone. It will be apparent that the forward angle is dependent upon the relative positions of the lens 24, the annular slit 29 and the light-sensitive element or cathode 32a of the tube 32. With the construction described, light striking the cathode 32a of the tube 32 in appreciable quantity will, due to the design of the lens and slit system, come from a narrow region bounded by two conical surfaces and inclined forward. It will be understood that the forward angle may be varied to suit particular conditions.

The percent ligh signal may be expressed as the fraction or percent peak signal relative to the background light level. The sensitivity is defined as the voltage output at the thyratron grid a, divided by the peak percent light signa. The threshold is defined as the peak percent light signal required to trigger the thyratron 85. Sensitivity and threshold are dependent upon the form of signal, but for any given form of signal the threshold, T, and sensitivity, S, are related as follows:

where C is the thyratron bias voltage, Vg(crit.) is the critical bias at whichthe thyratron fires, and V(crit.) is the critical signal required to fire the thyratron.

When the bomb approaches a target, such as an airplane, 4a certain amount of sky light which would otherwise reach the light-sensitive tube` 32 through the lens 24 is obscured by the airplane, and a sudden reduction of electron output from the light-sensitive cathode of the tube 32 occurs, since the bomb is traveling at high speed. This sudden decrease of electron emission from the cathode of the tube 32 results in a current pulse or a change in the bias on grid 82a of the first amplifier tube 812. This current pulse is amplified by the tubes 82, 83 and 84, and the amplified pulse acts on the control grid 85a of the thyratron to cause the latter suddenly to become conducting and fire the detonator 107. Preferably, the electrical components are so designed that the thyratron 85 will be triggered when the light reaching the light-sensitive tube 32 is reduced by even as little as one percent, due to interception of some of the light by the target.

For test purposes, we provide a conductor 117 connected between the control grid 85a of the thyratron and the adjacent coupling condenser 90b and leading to a contact 118 mounted in a receptacle 118a (Figure 5) accessible from outside the casing 20. An additional test wire 119 is connected between contact 55a of the self-destruction switch and resistor 108 and leads to a contact 120 mounted in a plug 120a (Figure 5) accessible from outside the casing through a removable cap 121.

The new light-sensitive fuze, in combination with an explosive projectile, provides an effective weapon for attacking and destroying enemy aircraft. In addition,

the fuze may be used in causing bombs to explode on ground approach, so that the fragments will be scattered downward for greater destructive eiect.

We claim: .A v

l. In a proximity fuze, a cylindrical shaped lens, a photoelectric'cell mounted within said lens,Y an opaque shield between said lens and saidcell and having a generally annular light-transmitting zone substantially surrounding said cell to admit light from said lens to said cell, and means for connecting saidcell into an electrical circuit. Y Y

2. In a proximity fuze, a casing, a cylindrical shaped lens carried by said casing, a photoelectric cell mounted within said lens, an electrical ampliiierA in said casing connected with'lsaid cell; and an opaque shield between said lens and said cell and having a: generally annular light-transmittingzone substantially surrounding said Vcell to adn'iit'light froni said lens to said cell.

3. Ina proximity fuze, a toroidal lens, a photoelectric cell mounted within said lens, means Vfor connecting said cell into an electrical circuit, and an apertured shield disl posed between said lens and said cell and substantially surrounding said cell to'admit light from said lens to said cell, said aperture and said lens deiining a zone of maximum light transmission to said cell.

4. In aV proximity fuze, a toroidal lens, a 'photoelectric cell mounted within said lens, means for connecting said cell into an electrical circuit, and an apertured opaque shield adjacent said lens and substantially surroundingl said cell to admit light from said lens to said cell, said aperture and lens defining a conically'V shapedV Zone of maximum light transmission to said cell. i

5. In a proximity fuze, a toroidal lens, and a photoelectric cell mounted within said lens in such a position to receive light from said lens through substantially 360 around said cell.

6. In a proximity Vfuze, a casing, a toroidal lens mounted on said casing, a photoelectric cell adjacent said lens, means for connecting said cell into an electrical cir,- cuit,V and an apertured opaque shield disposed between said lens and said cell to admit light from said lens to said cell, said aperture being in a surface of revolution about said axis of said lens.

' 7. In a proximity fuze, a casing, a toroidal lens mounted on said casing, a photoelectric celll located within said lens, an-apertured opaque shield within said lens between said lens and said cell and substantially surrounding said cell,` and means for connecting said cell into an electrical circuit. Y

8. In a proximity fuze, a casini a toroidal lens mounted on said casing, a photoelectric cell adjacent said lens' passing through, the axis of said casing, and a photoelectric cell disposed coaxially with respect to said lens.

10. In a proximity fuze, a lcasing, a toroidal lens on said casing and having an outer elliptical curvature in a plane passing through Vthe axis of said casing, an opaque shield.. adjacent said lens and having an aperture, a photo.

sensitive element disposed coaxially with respect to said lens and kadapted to receive light passing through said lensj and said aperture, and means for connecting said photosensitive element into an electrical circuit. Y l

1l. InV a VAphotoelectric proximity fuze, a photoelectric unit comprising a'pair of casing sections, a toroidal lens disposed between Ysaid vsections and maintaining said sections in spaced opposed relation to expose part of said lens, an inwardly extending sleeve on each o f said sections, said sleeves terminating in closely spaced relation to define a generally annular slit, and a photoelectric cell mounted in said sleeves and adapted to receive light passing through said lens and said slit.

l2. In a photoelectric proximity fuze, a photoelectric unitcomprising a pair of casing sections, a toroidal. lens.

disposed between said sectionsand maintaining said sections in'spaced opposed relation to expose part of said lens, an inwardly extending sleeve on each of said sec.

tions, said sleeves terminating in closely spaced relation to define a generally annular slit, a photoelectric cell, and cushioning means for mounting said cell in said sleeves whereby said cell is adapted to receive light through said lens and said slit.

ReferencesV Cited in the le of this patent -UNITED STATES PATENTS 2,013,594v zworyken' ,--v sept. '5,' 1935 2,164,916 `Immonet July 4, 1939 2,355,014 t Schorn Aug. 1, 1944 

